One-piece coupling



FIG. 1 is a perspective view of a one-piece coupling showing our new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The portions of the one-piece coupling shown in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a one-piece coupling, as shown and described. 